Is it possible to define a generic enum ?

[szagi3891]

I would like to define a generic enum that I will use in the openapi specification.

I tried to define it this way:

use poem_openapi::{OneOf, Object};
use poem_openapi::types::ToJSON;

#[derive(Debug, Object)]
pub struct ProxyResponseOk<R: Send + ToJSON> {
    pub response: R
}

#[derive(Debug, Object)]
pub struct ProxyResponseMessage {
    pub code: String,
    pub message: String,
}

#[derive(Debug, Object)]
pub struct ProxyResponseUnknown {
    pub code: u32,
    pub body: String,
}

#[derive(Debug, OneOf)]
#[oai(property_name="type")]
pub enum ProxyResponse<R: Send + ToJSON> {
    Ok(ProxyResponseOk<R>),
    Error(ProxyResponseMessage),
    Unknown(ProxyResponseUnknown),
}

When trying to compile I get errors:

error[E0412]: cannot find type `R` in this scope
  --> src/proxy/handler/selection_errors.rs:25:24
   |
22 | #[derive(Debug, OneOf)]
   |                      - help: you might be missing a type parameter: `<R>`
...
25 |     Ok(ProxyResponseOk<R>),
   |                        ^ not found in this scope

error[E0107]: missing generics for enum `ProxyResponse`
  --> src/proxy/handler/selection_errors.rs:24:10
   |
24 | pub enum ProxyResponse<R: Send + ToJSON> {
   |          ^^^^^^^^^^^^^ expected 1 generic argument
   |
note: enum defined here, with 1 generic parameter: `R`
  --> src/proxy/handler/selection_errors.rs:24:10
   |
24 | pub enum ProxyResponse<R: Send + ToJSON> {
   |          ^^^^^^^^^^^^^ -
help: add missing generic argument
   |
24 | pub enum ProxyResponse<R><R: Send + ToJSON> {
   |          ~~~~~~~~~~~~~~~~

Can I ask for help?

[sunli829]

Currently not supported, I will add it later.

[sunli829]

I've added support for generic union in v1.3.27, both inline and non-inline, non-inline requires specifying the name of the concrete type.

• inline example:

  poem/poem-openapi/tests/union.rs

  Line 452 in 3efbd92

  async fn inline_generic() {

• non-inline example:

  poem/poem-openapi/tests/union.rs

  Line 467 in 3efbd92

  async fn concrete_types() {

[szagi3891]

There is only one problem:

warning: `example-openapi-oneof` (bin "example-openapi-oneof") generated 6 warnings
    Finished dev [unoptimized + debuginfo] target(s) in 1.52s
     Running `target/debug/example-openapi-oneof`
thread 'main' panicked at '`example_openapi_oneof::ProxyResponse<alloc::string::String>` and `example_openapi_oneof::ProxyResponse<u32>` have the same OpenAPI name `ProxyResponse`', /Users/grzegorzszeliga/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/poem-openapi-1.3.27/src/registry/mod.rs:652:25
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Here is the code that demonstrates this problem

https://github.com/szagi3891/poem-test/blob/master/src/main.rs#L148

[sunli829]

If the object is generic, either specify the inline attribute to avoid creating the object in the schema. Either use concrete to give each concrete type a name.

I'll add a validator to catch this problem at compile time.

[szagi3891]

I understand. Would it be possible to make the inline attribute default to a type that is generic?

[szagi3891]

#[derive(Debug, Object)]
#[oai(inline)]
pub struct ProxyResponseOk<R: Send + ToJSON + ParseFromJSON> {
    pub response: R
}

#[derive(Debug, Object)]
pub struct ProxyResponseMessage {
    pub code: String,
    pub message: String,
}

#[derive(Debug, Object)]
pub struct ProxyResponseUnknown {
    pub code: u32,
    pub body: String,
}

#[derive(Debug, Union)]
#[oai(discriminator_name="type")]
#[oai(inline)]
pub enum ProxyResponse<R: Send + ToJSON + ParseFromJSON> {
    Ok(ProxyResponseOk<R>),
    Error(ProxyResponseMessage),
    Unknown(ProxyResponseUnknown),
}

Well, and if inline was added by default for types that have a generic parameter, it should nicely simplify this code.

[sunli829]

This is a breaking change 😂, I've improved it now, if you don't specify the inline or concretes attribute of the generic object, it will report an explicit error at compile time.

[sunli829]

Inline objects have the disadvantage that they cannot refer to themselves.

[szagi3891]

This message at compile time will be very helpful.

This is a breaking change.

Why is this a breaking change ? Until now, generic types have not been generated in the openapi specification (I guess).

[sunli829]

Why is this a breaking change ? Until now, generic types have not been generated in the openapi specification (I guess).

For poem-openapi. 🙂

[sunli829]

Fixed in v1.3.28

[szagi3891]

Thank you very much :)